The present invention pertains to a prosthetic foot, which has a core extended in the region of the instep and ankle and an elastic material enclosing the core.
In known prosthetic feet, the core is made of incompressible material and has a sloped bottom side to which a wedge-shaped heel of soft elastic material is attached. A sole of synthetic material with a toe portion is attached to the wedge-shaped heel.
The prosthetic feet, which have no ankle pivot, have been known for years. To achieve a natural walk, despite the lack of the ankle pivot, a prosthetic foot has been suggested, which is composed of several portions. One of the prosthetic feet is disclosed, for example, in U.S. Pat. No. 3,098,239. This known prosthetic foot, namely, the solid ankle-cushion heel prosthetic foot, is comprised of a heel, having a bottom surface sloping forwardly and downwardly from the elevated rear end, an upper foot portion, formed of a tough, but resilient material, and overlying the forward portion and sides of the heel, a horizontal sole portion, formed of resilient material having a density less than that of the upper portion, and a wedge-shaped heel portion of resilient material, having a density less than that of the sole portion. In this known structure, the soft elastic wedge-shaped heel portion serves the purpose of simulating a soft application of the foot and the rolling motion, which in the case of the natural foot are obtained by the ankle pivot.
The synthetic plastic material which forms the wedge-shaped heel portion must be, therefore, sufficiently soft to press the foot in its application and to make the rolling function of the foot possible. On the other hand, this material must be sufficiently hard to ensure a sufficient stability during walking. The sole portion, formed of the hard material, serves for producing the most elastic steps possible, whereas the upper portion is formed substantially of a medium-hard hydrolysis-resistant material and thus must protect the foot structure.
The known construction of the foot prosthesis for simulating a rolling motion has been used and has been further developed without, however, substantial changes. The disadvantage of this known construction is that the wedge-shaped heel portion and the sole are made of an absorbent and porous foam material, through which undesired chemical substances can be sucked when the sole comes in contact with moisture. A user of the prosthetic foot must be always very careful while walking to prevent lowering of the prosthetic foot into the environment which might include moisture and chemical substances. This substantially limits the freedom of walking by the user of the foot prosthesis.